Lubricating oil composition

ABSTRACT

A method of reducing deposits in an internal combustion engine, comprising lubricating the internal combustion engine with a lubricating oil composition comprising lubricating oil base oil, one or more anti-wear additives and one or more poly(hydroxycarboxylic acid) amide salt derivatives preparable by reaction of an amine and a poly(hydroxycarboxylic acid) of formula (I) 
 
Y—CO[O-A-CO] n —OH   (I) 
where Y is hydrogen or optionally substituted hydrocarbyl group, A is a divalent optionally substituted hydrocarbyl group and n is from 1 to 100, with an acid or a quaternizing agent.

RELATED CASES

The present application claims priority from EPC application 06252350.1, filed May 3, 2006, which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a lubricating oil composition for particular use in internal combustion engines.

BACKGROUND OF THE INVENTION

It will be appreciated that the same lubricating oils are not always used by consumers as internal combustion engine oils in their vehicles. As different lubricating oil compositions have differing abilities to suppress internal combustion engine fouling, this changing of oils may lead to the build-up of deposits such as sludge, varnish and soot-related deposits in an internal combustion engine.

Sludge and varnish deposits form through complex interactions of lubricating oil composition components with contaminants under differing engine conditions. Under low temperature operating conditions, such as short automotive trips, a lubricating oil composition may not get hot enough for contaminants such as water and fuel components to evaporate. At high temperatures a lubricating oil composition can oxidise, producing reactive groups and thickening. These conditions promote reactions with unburnt and partially burnt fuel, water, soot, acids, blow-by gases and other contaminants to form sludges and varnish. Also, if high levels of soot are not efficiently dispersed, then the soot particles can aggregate, forming extended structures and gels which increase the low shear viscosity of a lubricating oil composition. Such materials can build up to coat engine components and block vital oilways, potentially causing oil starvation and wear.

WO-A-2005/073551 discloses a non-metal containing lubricating oil additive which is said to have good cleaning performance and a lubricating oil composition comprising the same.

Said additive is characterised by containing a quaternary ammonium salt having a base number of at least 10 mg KOH/g. Examples of said additive are said to include quaternary ammonium salts obtained through salt-exchange of counter-anions contained in cationic surfactants such as tetra alkyl ammonium chloride and tetra alkyl ammonium sulfate.

EP-A-0194718 discloses lubricating oil compositions that contain one or more lubricating oils, one or more basic salts of polyvalent metals, and one or more polyesters or salts thereof which are either derived from one or more hydroxycarboxylic acids of the general formula HO—X—COOH, wherein X represents a bivalent saturated or unsaturated aliphatic radical which contains at least 8 carbon atoms and in which at least 4 carbon atoms are situated between the hydroxyl group and the carboxyl group, or derived from a mixture of one or more such hydroxycarboxylic acids and one or more carboxylic acids containing no hydroxyl groups.

The polyesters present in said lubricating oil composition are said to lead to a marked improvement in stability of the one or more basic salts in the lubricating oil composition. In addition, said polyesters are also said to have a cleansing effect which renders them capable of suppressing fouling of an internal combustion engine.

Despite such assertions, it remains highly desirable to develop lubricating oil compositions that not only exhibit outstanding abilities to suppress internal combustion engine fouling during continual use, but which also exhibit excellent cleaning performance in reducing deposits in the oil circuit of an internal combustion engines.

SUMMARY OF THE INVENTION

In some embodiments, the present invention relates to a lubricating oil composition comprising lubricating oil base oil, one or more anti-wear additives and one or more poly(hydroxycarboxylic acid) amide salt derivatives preparable by reaction of an amine and a poly(hydroxycarboxylic acid) of formula (I) Y—CO[O-A-CO]_(n)—OH   (I) wherein Y is hydrogen or optionally substituted hydrocarbyl group, A is a divalent optionally substituted hydrocarbyl group and n is from 1 to 100, with an acid or a quaternizing agent.

In other embodiments, the invention relates to a method for reducing deposits in an internal combustion engine using a lubricating oil in accordance with embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed understanding of the invention, reference is made to the accompanying Figures, in which:

FIG. 1 represents graphically the % increase in cleanliness ratings over the cleanliness ratings at 0 days for the results of Table 3;

FIG. 2 represents graphically the % increase in cleanliness ratings over the cleanliness ratings at 0 days for the results of Table 4; and

FIG. 3 represents graphically the % increase in cleanliness ratings over the cleanliness ratings at 0 hours for the results of Table 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Typical industry recognised methods to assess the cleanliness of an engine are based on deposit rating systems. Such systems typically use a numeric scale from 1 to 10 to define the level of cleanliness, wherein a rating of 10 is defined as completely clean.

The ability of a lubricating oil composition to suppress internal combustion engine fouling during continual use (i.e. “keep clean”) can be observed as the rating being maintained at the same level. Similarly, the ability of a lubricating oil composition to exhibit “cleaning” (i.e. “clean-up”) performance in reducing deposits is observed as an increase in the rating. “Continual cleansing” by a lubricating oil composition is observed by increasing ratings during the test. “End of test clean-up” is defined as the increase in rating between the start and end of test.

There has been surprisingly found in the present invention a lubricating oil composition for particular use in internal combustion engines, which lubricating oil composition not only suppresses internal combustion engine fouling and which also exhibits advantageous cleaning performance in the reduction of deposits such as sludge and varnish.

Accordingly, the present invention provides a lubricating oil composition comprising lubricating oil base oil, one or more anti-wear additives and one or more poly(hydroxycarboxylic acid) amide salt derivatives preparable by reaction of an amine and a poly(hydroxycarboxylic acid) of formula (I) Y—CO[O-A-CO]_(n)—OH   (I) wherein Y is hydrogen or optionally substituted hydrocarbyl group, A is a divalent optionally substituted hydrocarbyl group and n is from 1 to 100, preferably from 1 to 10, with an acid or a quaternizing agent.

As used herein, the term “hydrocarbyl” represents a radical formed by removal of one or more hydrogen atoms from a carbon atom of a hydrocarbon (not necessarily the-same carbon atoms in case more hydrogen atoms are removed). Hydrocarbyl groups may be aromatic, aliphatic, acyclic or cyclic groups. Preferably, hydrocarbyl groups are aryl, cycloalkyl, alkyl or alkenyl, in which case they may be straight-chain or branched-chain groups.

Representative hydrocarbyl groups include phenyl, naphthyl, methyl, ethyl, butyl, pentyl, methylpentyl, hexenyl, dimethylhexyl, octenyl, cyclooctenyl, methylcyclooctenyl, dimethylcyclooctyl, ethylhexyl, octyl, isooctyl, dodecyl, hexadecenyl, eicosyl, hexacosyl, triacontyl and phenylethyl.

In the present invention, the phrase “optionally substituted hydrocarbyl” is used to describe hydrocarbyl groups optionally containing one or more “inert” heteroatom-containing functional groups. By “inert” is meant that the functional groups do not interfere to any substantial degree with the function of the compound.

The optionally substituted hydrocarbyl group Y in formula (I) herein is preferably aryl, alkyl or alkenyl containing up to 50 carbon atoms, more preferably in the range of from 7 to 25 carbon atoms. For example, the optionally substituted hydrocarbyl group Y may be conveniently selected from heptyl, octyl, undecyl, lauryl, heptadecyl, heptadenyl, heptadecadienyl, stearyl, oleyl and linoleyl. Other examples of said optionally substituted hydrocarbyl group Y in formula (I) herein include C₄₋₈ cycloalkyls such as cyclohexyl; polycycloalkyls such as polycyclic terpenyl groups which are derived from naturally occurring acids such as abietic acid; aryls such as phenyl; aralkyls such as benzyl; and polyaryls such as naphthyl, biphenyl, stibenyl and phenylmethylphenyl.

In the present invention, the optionally substituted hydrocarbyl group Y may contain one or more functional groups such as carbonyl, carboxyl, nitro, hydroxy, halo, alkoxy, tertiary amino (no N—H linkages), oxy, cyano, sulfonyl and sulfoxyl. The majority of the atoms, other than hydrogen, in substituted hydrocarbyl groups are generally carbon, with the heteroatoms (e.g., oxygen, nitrogen and sulfur) generally representing only a minority, about 33% or less, of the total non-hydrogen atoms present.

Those skilled in the art will appreciate that functional groups such as hydroxy, halo, alkoxy, nitro and cyano in a substituted hydrocarbyl group Y will displace one of the hydrogen atoms of the hydrocarbyl, whilst functional groups such as carbonyl, carboxyl, tertiary amino (—N—), oxy, sulfonyl and sulfoxyl in a substituted hydrocarbyl group will displace a —CH— or —CH₂— moiety of the hydrocarbyl.

The hydrocarbyl group Y in formula (I) is more preferably unsubstituted or substituted by a group selected from hydroxy, halo or alkoxy group, even more preferably C₁₋₄ alkoxy. Most preferably, the optionally substituted hydrocarbyl group Y in formula (I) is a stearyl group, 12-hydroxystearyl group, an oleyl group, a 12-hydroxyoleyl group or a group derived from naturally occurring oil such as tall oil fatty acid.

In a preferred embodiment of the present invention, the one or more poly(hydroxy-carboxylic acid) amide salt derivatives are sulfur-containing poly(hydroxycarboxylic acid) amide salt derivatives. More preferably, said one or more poly(hydroxycarboxylic acid) amide salt derivatives have a sulfur content in the range of from 0.1 to 2.0 wt. %, even more preferably in the range of from 0.6 to 1.2 wt. % sulfur, as measured by ICP-AES, based on the total weight of said poly(hydroxycarboxylic acid) amide salt derivatives. The preparation of poly(hydroxycarboxylic acid) and its amide or other derivatives is known and is described, for instance, in EP-A-0164817, WO-A-95/17473, WO-A-96/07689, U.S. Pat. No. 5,536,445, GB-A-2001083, GB-A-1342746, GB-A-1373660, US-A-5000792 and U.S. Pat. No. 4,349,389.

The poly(hydroxycarboxylic acid)s of formula (I) may be made by the interesterification of one or more hydroxycarboxylic acids of formula (II) HO-A-COOH   (II) wherein A is a divalent optionally substituted hydrocarbyl group, optionally in the presence of a catalyst according to well known methods. Such methods are described, for example, in U.S. Pat. No. 3,996,059, GB-A-1373660 and GB-A-1342746.

The chain terminator in said interesterification may be a non-hydroxycarboxylic acid. The hydroxyl group in the hydroxycarboxylic acid and the carboxylic acid group in the hydroxycarboxylic acid or the non-hydroxycarboxylic acid may be primary, secondary or tertiary in character.

The interesterification of the hydroxycarboxylic acid and the non-hydroxycarboxylic acid chain terminator may be effected by heating the starting materials, optionally in a suitable hydrocarbon solvent such as toluene or xylene, and azeotroping off the formed water. The reaction may be carried out at a temperature up to -250° C, conveniently at the reflux temperature of the solvent.

Where the hydroxyl group in the hydroxycarboxylic acid is secondary or tertiary, the temperature employed should not be so high as to lead to dehydration of the acid molecule.

Catalysts for the interesterification, such as p-toluenesulfonic acid, zinc acetate, zirconium naphthenate or tetrabutyl titanate, may be included, with the objective of either increasing the rate of reaction at a given temperature or of reducing the temperature required for a given rate of reaction.

In the compounds of formulae (I) and (II), A is preferably an optionally substituted aromatic, aliphatic or cycloaliphatic straight chain or branched divalent hydrocarbyl group. Preferably, A is an arylene, alkylene or alkenylene group, in particular an arylene, alkylene or alkenylene group containing in the range of from 4 to 25 carbon atoms, more preferably in the range of from 12 to 20 carbon atoms. Preferably, in said compounds of formulae (I) and (II), there are at least 4 carbon atoms, more preferably in the range of from 8 to 14 carbon atoms connected directly between the carbonyl group and the oxygen atom derived from the hydroxyl group.

In the compounds of formulae (I) and (II), the optional substituents in the group A are preferably selected from hydroxy, halo or alkoxy groups, more preferably C₁₋₄ alkoxy groups. The hydroxyl group in the hydroxycarboxylic acids of formula (II) is preferably a secondary hydroxyl group. Examples of suitable hydroxycarboxylic acids are 9-hydroxystearic acid, 10-hydroxystearic acid, 12-hydroxystearic acid, 12-hydroxy-9-oleic acid (ricinoleic acid), 6-hydroxycaproic acid, preferably 12-hydroxystearic acid. Commercial 12-hydroxystearic acid (hydrogenated castor oil fatty acid) normally contains up to 15% wt of stearic acid and other non-hydroxycarboxylic acids as impurities and can conveniently be used without further admixture to produce a polymer of molecular weight about 1000-2000.

Where the non-hydroxycarboxylic acid is introduced separately to the reaction, the proportion which is required in order to produce a polymer or oligomer of a given molecular weight can be determined either by simple experiment or by calculation by the person skilled in the art.

The group (—O-A-CO—) in the compounds of formulae (I) and (II) is preferably a 12-oxystearyl group, 12-oxyoleyl group or a 6-oxycaproyl group. Preferred poly(hydroxycarboxylic acid)s of formula (I) for reaction with amine include poly(hydroxystearic acid) and poly(hydroxyoleic acid). The amines which react with poly(hydroxycarboxylic acid)s of formula (I) to form poly(hydroxycarboxylic acid) amide intermediates may include those defined in WO-A-97/41092. For example, various amines and their preparations are described in U.S. Pat. No. 3,275,554, U.S. Pat. No. 3,438,757, U.S. Pat. No. 3,454,555, U.S. Pat. No. 3,565,804, U.S. Pat. No. 3,755,433 and U.S. Pat. No. 3,822,209.

The amine reactant is preferably a diamine, a triamine or a polyamine. Preferred amine reactants are diamines selected from ethylenediamine, N,N-dimethyl-1,3-propanediamine, triamines and polyamines selected from dietheylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine and tris(2-aminoethyl)amine. The amidation between the amine reactant and the (poly(hydroxycarboxylic acid) of formula (I) may be carried out according to methods known to those skilled in the art, by heating the poly(hydroxycarboxylic acid) with the amine reactant, optionally in a suitable hydrocarbon solvent such as toluene or xylene, and azeotroping off the formed water. Said reaction may be carried out in the presence of a catalyst such as p-toluenesulfonic acid, zinc acetate, zirconium naphthenate or tetrabutyl titanate.

Various patent documents disclose poly(hydroxycarboxylic acid) amide derivatives. For instance, GB-A-1373660 discloses poly(hydroxycarboxylic acid) amide derivatives with amines such as 3-dimethylaminopropylamine and ethylenediamine for use as dispersing agents in dispersions of pigments in organic liquids. GB-A-2001083 discloses poly(hydroxycarboxylic acid) amide derivatives with poly(ethyleneimine) (PEI) having a molecular weight (MW) greater than 500 for a similar use. In U.S. Pat. No. 5000792, poly(hydroxycarboxylic acid) amide derivatives with amines of the formula of NH₂—R′—N(R″)—R′″—NH₂ are disclosed for use as pigment dispersing agent. WO-A-95/17473 discloses poly(hydroxycarboxylic acid) amide derivatives with amines such as 3-dimethylaminopropylamine, ethylenediamine, poly(ethyleneimine) (PEI) having a molecular weight (MW) greater than 500 and amines of the formula of NH₂—R′—N(R″)—R′″—NH₂ for use in a method of preparing a non-aqueous dispersion of copper phthalocyanine.

U.S. Pat. No. 4,349,389 discloses poly(hydroxycarboxylic acid) amide derivatives with amines such as 3-dimethyl-aminopropylamine, poly(ethyleneimine) (PEI) having a molecular weight (MW) greater than 500 as dispersing agent in the preparation of a dispersible inorganic pigment composition. EP-A-0164817 discloses poly(hydroxycarboxylic acid) amide derivatives with polyamines (ethylenediamine, diethylenetriamine, etc.), aminoalcohols (diethanolamine, etc.) and ester derivatives with polyols (glycerol, etc.) for use as surfactant suitable for stabilising dispersions of solids in organic liquids and oil/water emulsions.

However, none of the afore-mentioned patent documents disclose the use of one or more poly(hydroxycarboxylic acid) amide salt derivatives as disclosed herein in lubricating oil compositions. The poly(hydroxycarboxylic acid) amide intermediate formed from reaction of the amine and the poly(hydroxycarboxylic acid) of formula (I) is reacted with an acid or a quaternizing agent to form a salt derivative, according to well-known methods.

Acids that may be used to form the salt derivative may be selected from organic or inorganic acids. Said acids are preferably sulfur-containing organic or inorganic acids. Preferably, said acids are selected from sulfuric acid, methanesulfonic acid and benzenesulfonic acid.

Quaternizing agents that may be used to form the salt derivative may be selected from dimethylsulfuric acid, a dialkyl sulfate having from 1 to 4 carbon atoms, an alkyl halide such as methyl chloride, methyl bromide, aryl halide such as benzyl chloride. In a preferred embodiment of the present invention, the quaternizing agent is a sulfur-containing quaternizing agent, in particular dimethylsulfuric acid or an dialkyl sulfate having from 1 to 4 carbon atoms. The quaternizing agent is preferably dimethyl sulfate. Quaternization is a well-known method in the art. For example, quaternization using dimethyl sulfate is described in U.S. Pat. No. 3,996,059, U.S. Pat. No. 4,349,389 and GB-A-1373660.

In a preferred embodiment of the present invention, the one or more poly(hydroxycarboxylic acid) amide salt derivatives comprise a compound of formula (III): [Y—CO[O-A-CO]_(n)-Z-R⁺]_(m) pX^(q−)  (III) wherein Y is hydrogen or optionally substituted hydrocarbyl group, A is a divalent optionally substituted hydrocarbyl group, n is from 1 to 100, preferably from 1 to 10, m is from 1 to 4, q is from 1 to 4 and p is an integer such that pq=m, Z is an optionally substituted divalent bridging group which is attached to the carbonyl group through a nitrogen atom, R+is an ammonium group and X^(q−) is an anion. R⁺ may be a primary, secondary, tertiary or quaternary ammonium group and is preferably a quaternary ammonium group.

In formula (III), A is preferably a divalent straight chain or branched hydrocarbyl group as hereinbefore described for formulae (I) and (II). That is to say, in formula (III), A is preferably an optionally substituted aromatic, aliphatic or cycloaliphatic straight chain or branched divalent hydrocarbyl group. More preferably, A is an arylene, alkylene or alkenylene group, in particular an arylene, alkylene or alkenylene group containing in the range of from 4 to 25 carbon atoms, more preferably in the range of from 12 to 20 carbon atoms.

Preferably, in said compound of formula (III), there are at least 4 carbon atoms, more preferably in the range of from 8 to 14 carbon atoms connected directly between the carbonyl group and the oxygen atom derived from the hydroxyl group.

In the compound of formula (III), the optional substituents in the group A are preferably selected from hydroxy, halo or alkoxy groups, especially C₁₋₄ alkoxy groups.

In formula (III), Y is preferably an optionally substituted hydrocarbyl group as hereinbefore described for formula (I). That is to say, the optionally substituted hydrocarbyl group Y in formula (III) is preferably aryl, alkyl or alkenyl containing up to 50 carbon atoms, more preferably in the range of from 7 to 25 carbon atoms. For example, the optionally substituted hydrocarbyl group Y may be conveniently selected from heptyl, octyl, undecyl, lauryl, heptadecyl, heptadenyl, heptadecadienyl, stearyl, oleyl and linoleyl.

Other examples of said optionally substituted hydrocarbyl group Y in formula (III) herein include C₄-₈ cycloalkyls such as cyclohexyl; polycycloalkyls such as polycyclic terpenyl groups which are derived from naturally occurring acids such as abietic acid; aryls such as phenyl; aralkyls such as benzyl; and polyaryls such as naphthyl, biphenyl, stibenyl and phenylmethylphenyl.

In the present invention, the optionally substituted hydrocarbyl group Y in formula (III) may contain one or more functional groups such as carbonyl, carboxyl, nitro, hydroxy, halo, alkoxy, amino, preferably tertiary amino (no N-H linkages), oxy, cyano, sulfonyl and sulfoxyl. The majority of the atoms, other than hydrogen, in substituted hydrocarbyl groups are generally carbon, with the heteroatoms (e.g., oxygen, nitrogen and sulfur) generally representing only a minority, about 33% or less, of the total non-hydrogen atoms present.

Those skilled in the art will appreciate that functional groups such as hydroxy, halo, alkoxy, nitro and cyano in a substituted hydrocarbyl group Y will displace one of the hydrogen atoms of the hydrocarbyl, whilst functional groups such as carbonyl, carboxyl, tertiary amino (—N—), oxy, sulfonyl and sulfoxyl in a substituted hydrocarbyl group will displace a —CH— or —CH₂— moiety of the hydrocarbyl. More preferably, the hydrocarbyl group Y in formula (III) is unsubstituted or substituted by a group selected from hydroxy, halo or alkoxy group, even more preferably C₁₋₄ alkoxy. Most preferably, the optionally substituted hydrocarbyl group Y in formula (III) is a stearyl group, 12-hydroxystearyl group, an oleyl group or a 12-hydroxyoleyl group, and that derived from naturally occurring oil such as tall oil fatty acid.

In formula (III), Z is preferably an optionally substituted divalent bridging group represented by formula (IV)

wherein R¹ is hydrogen or a hydrocarbyl group and B is an optionally substituted alkylene group.

Examples of hydrocarbyl groups that may represent R¹ include methyl, ethyl, n-propyl, n-butyl and octadecyl. Examples of optionally substituted alkylene groups that may represent B include ethylene, trimethylene, tetramethylene and hexamethylene.

Examples of preferred Z moieties in formula (III) include —NHCH₂CH₂— and —NHCH₂C(CH₃)₂CH₂— and —NH(CH₂)₃—.

Preferably, R⁺ may be represented by formula (V)

wherein R², R³ and R⁴ may be selected from hydrogen and alkyl groups such as methyl.

Preferably, the anion X^(q−) of the compound of formula (III) is a sulfur-containing anion. More preferably said anion is selected from sulfate and sulfonate anions.

The one or more poly(hydroxycarboxylic acid) amide salt derivatives are present in the lubricating oil composition of the present invention in a preferred amount in the range of from 0.1 to 10.0 wt. %, more preferably in an amount in the range of from 0.1 to 5.0 wt. % and most preferably in an amount in the range of from 0.2 to 4.0 wt. %, based on the total weight of the lubricating oil composition.

Poly(hydroxycarboxylic acid) amide salt derivatives that are preferred in the present invention are those which each have a TBN (total base number) value of less than 10 mg.KOH/g, as measured by ASTM D 4739. More preferably, the poly(hydroxycarboxylic acid) amide salt derivatives each have a TBN value of less than 5 mg.KOH/g, most preferably 2 mg.KOH/g or less, as measured by ASTM D 4739.

Examples of poly(hydroxycarboxylic acid) amide salt derivatives that are available commercially include that available from Lubrizol under the trade designation “SOLSPERSE 17000” (a reaction product of poly(12-hydroxystearic acid) with N,N-dimethyl-1,3-propanediamine and dimethyl sulfate) and those available under the trade designations “CH-5” and “CH-7” from Shanghai Sanzheng Polymer Company.

The one or more anti-wear additives in the lubricating oil composition of the present invention are preferably present in an amount in the range of from 0.01 to 10.0 wt. %, based on the total weight of the lubricating oil composition. Preferably, the one or more anti-wear additives present in the lubricating oil composition may comprise zinc dithiophosphates. The or each zinc dithiophosphate may be selected from zinc dialkyl-, diaryl- or alkylaryl-dithiophosphates. Preferred zinc dithiophosphates are those that may be conveniently represented by formula (VI):

wherein R⁵ to R⁸ may be the same or different and are each a primary alkyl group containing from 1 to 20 carbon atoms preferably from 3 to 12 carbon atoms, a secondary alkyl group containing from 3 to 20 carbon atoms, preferably from 3 to 12 carbon atoms, an aryl group or an aryl group substituted with an alkyl group, said alkyl substituent containing from 1 to 20 carbon atoms preferably 3 to 18 carbon atoms.

Zinc dithiophosphate compounds in which R⁵ to R⁸ are all different from each other can be used alone or in admixture with zinc dithiophosphate compounds in which R⁵ to R⁸ are all the same. Preferably, the or each zinc dithiophosphate used in the present invention is a zinc dialkyl dithiophosphate.

Examples of zinc dithiophosphates which are commercially available include those available ex. Lubrizol Corporation under the trade designations “Lz 677A”, “Lz 1095”, “Lz 1097”, “Lz 1370”, “Lz 1371”, “Lz 1373” and “Lz 1395”, those available ex. Chevron Oronite under the trade designations “OLOA 260”, “OLOA 262”, “OLOA 267” and “OLOA 269R”, and those available ex. Afton Chemical under the trade designation “HITEC 7169” and “HITEC 7197”.

The lubricating oil composition according to the present invention preferably comprises in the range of from 0.01 to 10.0 wt. % of zinc dithiophosphates, based on total weight of the lubricating oil composition. Additional or alternative anti-wear additives may be conveniently used in the lubricating oil composition of the present invention.

In a preferred embodiment of the present invention, the lubricating oil composition further comprises one or more detergents, in particular one or more salicylate, phenate or sulfonate detergents. Said detergents are preferably selected from alkali metal or alkaline earth metal salicylate, phenate or sulfonate detergents. Calcium and magnesium salicylates, phenates and sulfonates are particularly preferred. Said detergents are preferably used in amounts in the range of 0.05 to 12.5 wt. %, more preferably from 1.0 to 9.0 wt. % and most preferably in the range of from 2.0 to 5.0 wt. %, based on the total weight of the lubricating oil composition.

There are no particular limitations regarding the base oil used in the present invention, and various conventional known mineral oils and synthetic oils may be conveniently used. The lubricating oil base oil used in the present invention may conveniently comprise mixtures of one or more mineral oils and/or one or more synthetic oils. Mineral oils include liquid petroleum oils and solvent-treated or acid-treated mineral lubricating oil of the paraffinic, naphthenic, or mixed paraffinic/naphthenic type which may be further refined by hydrofinishing processes and/or dewaxing.

Naphthenic base oils have low viscosity index (VI) (generally 40-80) and a low pour point. Such base oils are produced from feedstocks rich in naphthenes and low in wax content and are used mainly for lubricants in which colour and colour stability are important, and VI and oxidation stability are of secondary importance.

Paraffinic base oils have higher VI (generally >95) and a high pour point. Said base oils are produced from feedstocks rich in paraffins, and are used for lubricants in which VI and oxidation stability are important.

Fischer-Tropsch derived base oils may be conveniently used as the base oil in the lubricating oil composition of the present invention, for example, the Fischer-Tropsch derived base oils disclosed in EP-A-0776959, EP-A-0668342, WO-A-97/21788, WO-A-00/15736, WO-A-00/14188, WO-A-00/14187, WO-A-00/14183, WO-A-00/14179, WO-A-00/08115, WO-A-99/41332, EP-A-1029029, WO-A-01/18156 and WO-A-01/57166.

Synthetic processes enable molecules to be built from simpler substances or to have their structures modified to give the precise properties required. Synthetic oils include hydrocarbon oils such as olefin oligomers (PAOs), dibasic acid esters, polyol esters, and dewaxed waxy raffinate. Synthetic hydrocarbon base oils sold by the Shell Group under the designation “XHVI” (trade mark) may be conveniently used.

Preferably, the lubricating oil base oil is constituted from mineral oils and/or synthetic oils which contain more than 80% wt of saturates, preferably more than 90 % wt., as measured according to ASTM D2007.

It is further preferred that the lubricating oil base oil contains less than 1.0 wt. %, preferably less than 0.1 wt. % of sulfur, calculated as elemental sulfur and measured according to ASTM D2622, ASTM D4294, ASTM D4927 or ASTM D3120. Preferably, the viscosity index of the lubricating oil base oil is more than 80, more preferably more than 120, as measured according to ASTM D2270.

The total amount of lubricating oil base oil incorporated in the lubricating oil composition of the present invention is preferably present in an amount in the range of from 60 to 92 wt. %, more preferably in an amount in the range of from 75 to 90 wt. % and most preferably in an amount in the range of from 75 to 88 wt. %, with respect to the total weight of the lubricating oil composition.

Preferably, the lubricating oil composition has a kinematic viscosity in the range of from 2 to 80 mm²/s at 100 ° C., more preferably in the range of from 3 to 70 mm²/s, most preferably in the range of from 4 to 50 mm²/s.

The lubricating oil composition of the present invention may further comprise additional additives such as anti-oxidants, dispersants, friction modifiers, viscosity index improvers, pour point depressants, corrosion inhibitors, defoaming agents and seal fix or seal compatibility agents.

Antioxidants that may be conveniently used include those selected from the group of aminic antioxidants and/or phenolic antioxidants. In a preferred embodiment, said antioxidants are present in an amount in the range of from 0.1 to 5.0 wt. %, more preferably in an amount in the range of from 0.3 to 3.0 wt. %, and most preferably in an amount of in the range of from 0.5 to 1.5 wt. %, based on the total weight of the lubricating oil composition.

Examples of aminic antioxidants which may be conveniently used include alkylated diphenylamines, phenyl-α-naphthylamines, phenyl-β-naphthylamines and alkylated-naphthylamines. Preferred aminic antioxidants include dialkyldiphenylamines such as p,p′-dioctyl-diphenylamine, p,p′-di-α-methylbenzyl-diphenylamine and N-p-butylphenyl-N-p′-octylphenylamine, monoalkyldiphenylamines such as mono-t-butyldiphenylamine and mono-octyldiphenylamine, bis(dialkylphenyl)amines such as di-(2,4-diethylphenyl)amine and di(2-ethyl-4-nonylphenyl)amine, alkylphenyl-l-naphthylamines such as octylphenyl-1-naphthylamine and n-t-dodecylphenyl-1 -naphthylamine, 1-naphthylamine, arylnaphthylamines such as phenyl-1-naphthylamine, phenyl-2-naphthylamine, N-hexylphenyl-2-naphthylamine and N-octylphenyl-2-naphthylamine, phenylenediamines such as N,N′-diisopropyl-p-phenylenediamine and N,N′-diphenyl-p-phenylenediamine, and phenothiazines such as phenothiazine and 3,7-dioctylphenothiazine. Preferred aminic antioxidants include those available under the following trade designations: “Sonoflex OD-3” (ex. Seiko Kagaku Co.), “Irganox L-57” (ex. Ciba Specialty Chemicals Co.) and phenothiazine (ex. Hodogaya Kagaku Co.).

Examples of phenolic antioxidants which may be conveniently used include C₇-C₉ branched alkyl esters of 3,5-bis(1,1-dimethyl-ethyl)-4-hydroxy-benzenepropanoic acid, 2-t-butylphenol, 2-t-butyl-4-methylphenol, 2-t-butyl-5-methylphenol, 2,4-di-t-butylphenol, 2,4-dimethyl-6-t-butylphenol, 2-t-butyl-4-methoxyphenol, 3-t-butyl-4-methoxyphenol, 2,5-di-t-butylhydroquinone, 2,6-di-t-butyl-4-alkylphenols such as 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol and 2,6-di-t-butyl-4-ethylphenol, 2,6-di-t-butyl-4-alkoxyphenols such as 2,6-di-t-butyl-4-methoxyphenol and 2,6-di-t-butyl-4-ethoxyphenol, 3,5-di-t-butyl-4-hydroxybenzylmercaptooctylacetate, alkyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionates such as n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, n-butyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and 2′-ethylhexyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,6-d-t-butyl-α-dimethylamino-p-cresol, 2,2′-methylenebis(4-alkyl-6-t-butylphenol) such as 2,2′-methylenebis(4-methyl-6-t-butylphenol, and 2,2-methylenebis(4-ethyl-6-t-butylphenol), bisphenols such as 4,4′-butylidenebis(3-methyl-6-t-butylphenol, 4,4′-methylenebis(2,6-di-t-butylphenol), 4,4′-bis(2,6-di-t-butylphenol), 2,2-(di-p-hydroxyphenyl)propane, 2,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)propane, 4,4′-cyclohexylidenebis(2,6-t-butylphenol), hexamethyleneglycol-bis [3-(3,5-di-t-butyl-4-hydroxyphenyl)propionatel, triethyleneglycolbis [3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionatel, 2,2′-thio-[diethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 3,9-bis{1,1 -dimethyl-2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)-propionyloxylethyl}2,4,8,10-tetraoxaspiro[5,5]undecane, 4,4′-thiobis(3-methyl-6-t-butylphenol) and 2,2′-thiobis(4,6-di-t-butylresorcinol), polyphenols such as tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionatelmethane, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)-butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, bis-[3,3′-bis(4′-hydroxy-3′-t-butylphenyl)butyric acid]glycol ester, 2-(3′,5′-di-t-butyl-4-hydroxyphenyl)methyl-4-(2″,4″-di-t-butyl-3″-hydroxyphenyl)methyl-6-t-butylphenol and 2,6-bis(2′-hydroxy-3′-t-butyl-5′-methylbenzyl)-4-methylphenol, and p-t-butylphenol—formaldehyde condensates and p-t-butylphenol—acetaldehyde condensates.

Preferred phenolic antioxidants include those available under the following trade designations: “Irganox L-135” (ex. Ciba Specialty Chemicals Co.), “Yoshinox SS” (ex. Yoshitomi Seiyaku Co.), “Antage W-400” (ex. Kawaguchi Kagaku Co.), “Antage W-500” (ex. Kawaguchi Kagaku Co.), “Antage W-300” (ex. Kawaguchi Kagaku Co.), “Irganox L-109” (ex. Ciba Speciality Chemicals Co.), “Tominox 917” (ex. Yoshitomi Seiyaku Co.), “Irganox L-115” (ex. Ciba Speciality Chemicals Co.), “Sumilizer GA80” (ex. Sumitomo Kagaku), “Antage RC” (ex. Kawaguchi Kagaku Co.), “Irganox L-101” (ex. Ciba Speciality Chemicals Co.), “Yoshinox 930” (ex. Yoshitomi Seiyaku Co.).

The lubricating oil composition of the present invention may comprise mixtures of one or more phenolic antioxidants with one or more aminic antioxidants.

The lubricating oil compositions of the present invention may additionally contain an ash-free dispersant which is preferably admixed in an amount in the range of from 5 to 15 wt. %, based on the total weight of the lubricating oil composition. Examples of ash-free dispersants which may be used include the polyalkenyl succinimides and polyalkenyl succininic acid esters disclosed in Japanese Laid-Open Patent Application Nos. JP 53-050291 A, JP 56-120679 A, JP 53-056610 A and JP 58-171488 A. Preferred dispersants include borated succinimides.

Examples of viscosity index improver improvers which may conveniently be used in the lubricating oil composition of the present invention include the styrene-butadiene copolymers, styrene-isoprene stellate copolymers and the polymethacrylate copolymer and ethylene-propylene copolymers. Dispersant-viscosity index improvers may be used in the lubricating oil composition of the present invention. Such viscosity index improver improvers may be conveniently employed in an amount in the range of from 1 to 20 wt. %, based on the total weight of the lubricating oil composition.

Polymethacrylates may be conveniently employed in the lubricating oil compositions of the present invention as effective pour point depressants. Furthermore, compounds such as alkenyl succinic acid or ester moieties thereof, benzotriazole-based compounds and thiodiazole-based compounds may be conveniently used in the lubricating oil composition of the present invention as corrosion inhibitors. Compounds such as polysiloxanes, dimethyl polycyclohexane and polyacrylates may be conveniently used in the lubricating oil composition of the present invention as defoaming agents. Compounds which may be conveniently used in the lubricating oil composition of the present invention as seal fix or seal compatibility agents include, for example, commercially available aromatic esters.

The lubricating oil compositions of the present invention may be conveniently prepared by admixing the one or more anti-wear additives, one or more poly(hydroxycarboxylic acid) amide salt derivatives and, optionally, one or more detergents and further additives that are usually present in lubricating oil compositions, for example as herein before described, with mineral and/or synthetic base oil.

The present invention further provides a method of reducing deposits in an internal combustion engine, which method comprises lubricating said internal combustion engine with a lubricating oil composition as hereinbefore described. Furthermore, the present invention also provides for the use of a lubricating oil composition as hereinbefore described in order to reduce deposits in an internal combustion engine. In particular, the present invention provides a method of suppressing internal combustion engine fouling and/or improving cleaning performance in the reduction of deposits such as sludge and varnish.

Thus, the present invention further provides for the use of a lubricating oil composition as hereinbefore described in order to suppress internal combustion engine fouling and/or improve cleaning performance in the reduction of internal combustion engine deposits such as sludge and varnish.

There is further provided a method of lubricating an internal combustion engine comprising applying a lubricating oil composition as hereinbefore described thereto.

The present invention is described below with reference to the following Examples, which are not intended to limit the scope of the present invention in any way.

EXAMPLES

Lubricating Oil Compositions

Tables 1 and 2 indicate the lubricating oil compositions that were tested.

Poly(hydroxycarboxylic acid) amide salt derivatives according to the present invention that were used in testing were products available commercially from Lubrizol under the trade designation “SOLSPERSE 17000” (a reaction product of poly(12-hydroxystearic acid) with N,N-dimethyl-1,3-propanediamine and dimethyl sulfate) and under the trade designation “CH-7” from Shanghai Sanzheng Polymer Company. “SOLSPERSE 17000” product and “CH-7” product have TBN values of approximately 2.0 mg.KOH/g and 1.9 mg.KOH, respectively, as measured by ASTM D 4739. Furthermore, “SOLSPERSE 17000” product and “CH-7” product have sulfur contents of approximately 0.89 wt. % and 0.86 wt. %, respectively, as measured by ICP-AES.

A comparative product was tested which was a poly(hydroxycarboxylic acid) derivative that is not according to the teaching of the present invention. Said comparative product is available from commercially from Lubrizol under the trade designation “SOLSPERSE 11200”. “SOLSPERSE 11200” product has a TBN value of approximately 35 mg.KOH/g, as measured by ASTM D 4739 and a sulfur content of <0.01 wt. %, as measured by ICP-AES.

The formulation of Comparative Example 1 in Table 1 was a commercial engine oil which comprised API Group I base oil, pour point depressant, viscosity modifier, antifoam, a conventional additive package containing sulfonate and phenate detergents having TBNs in the range of from 30 to 350 mg.KOH/g, PIB succinimide dispersant and zinc dithiophosphate and diluent oil. Said formulation was also used as the basis for the formulations of Examples 2 and 3.

The formulation of Comparative Example 3 in Table 2 was a commercial engine oil which comprised base oil and zinc dithiophosphate anti-wear additive and conventional lubricant additives and is available from the Shell group under the trade designation “HELIX” engine oil. Said formulation was also used as the basis for the formulation of Example 4. TABLE 1 Comp. Comp. Additive (wt. %) Ex. 1 Ex. 2¹ Ex. 3¹ Ex. 1² Ex. 2 Anti-foam — 10 ppm 10 ppm 10 ppm — Additive package — 11.3 11.3 11.3 — Pour point depressant — 0.15 0.15 0.15 — Viscosity modifier — 6.2 6.2 6.2 — “SOLSPERSE 17000” 3.0 3.0 — — — product “SOLSPERSE 11200” — — — — 3.0 product “CH-7” product — — 3.0 — — API Group I Base Oil 97.0 79.35 79.35 82.35 97.0 TOTAL 100 100 100 100 100 ¹Lubricating oil composition of Comp. Ex. 1 with further “SOLSPERSE 17000” or “CH-7” products added. ²Commercial engine oil comprising a conventional additive package containing sulfonate and phenate detergents having TBNs in the range of from 30 to 350 mg · KOH/g, PIB succinimide dispersant and zinc dithiophosphate and diluent oil.

TABLE 2 Comp. Formulation/additive (wt. %) Ex. 4 Ex. 3 Commercial engine oil available from the Shell group 97.0 100.0 under the trade designation “HELIX” engine oil “CH-7” additive 3.0 — TOTAL 100 100 Modified Sequence VG Test

The modified Sequence VG test was performed as follows:

1. The “dirty-up” phase was conducted as per ASTM D6593, using a new VG engine and a “dirty-up” standard oil which was an API SF specification oil with the following modifications:

-   -   Intermediate sludge ratings of the right side of the engine were         carried out every 24 hours on the valve deck, cam cover and         cam-baffle.     -   Photographs were taken of each of these components every 24         hours.     -   The test was run until one of the components had accumulated         enough sludge and varnish to achieve a rating of         approximately 7. The time taken to reach this rating (˜7) was         approximately 216 to 288 hours.

2. At the end of the “dirty-up” phase, the “dirty-up” standard oil was drained. The “dirty-up” standard oil was then replaced with the lubricating oil composition to be tested and the engine was ready to continue with the second part of the test.

3. The second part of the test, the “clean-up” phase, was conducted in exactly the same manner as the “dirty-up” phase for the standard 216 hours. 24 hourly ratings and photographs were taken throughout the test.

4. Passing lubricating oil compositions tended to show an initial “cleaning” effect, followed by “continual cleansing”. For passing lubricating oil compositions, the average rating increased significantly during the first 24 hours of the “clean-up” phase and the final (216 hour) rating was higher than this “post-cleaning” rating.

Bench Screener Test

A bench screener test was developed in order to demonstrate deposit control specifically in relation to the ability of a lubricant to “clean-up” real engine sludge rather than just “keep clean.”

1. A cam-baffle was obtained from a VG engine after running the dirty-up phase of the modified Sequence VG test as described above.

2. 1 cm×1 cm samples were cut from the cam-baffle, using a lever-press to avoid contamination with cutting fluid.

3. Cam-baffle samples were dipped in lubricating oil compositions to be tested and allowed to drain before initial cleanliness ratings for sludge and varnish were made and photographs were taken for each sample.

4. Cam-baffle samples were then suspended in the lubricating oil compositions to be tested (100 g). The lubricating oil compositions were then stirred and maintained at 80° C. for a period of up to 14 days.

5. Cleanliness ratings and photographs were taken at intermediate time-intervals to assess the performance of the lubricating oil compositions tested.

A rating of 10.0 means that the sample was completely clean with no sludge or varnish thereon.

Results and Discussion

The formulations described in Tables 1 and 2 were tested using the afore-mentioned tests and the results obtained thereon are detailed below:

Testing using bench screener test

Example 1 and Comparative Examples 1 and 2

The lubricating oil compositions of Example 1 and Comparative Examples 1 and 2 were screened using the bench test screener test. Cleanliness ratings for the lubricating oil compositions of Example 1 and Comparative Example 2 were taken and compared against those of the fully formulated lubricating oil composition of Comparative Example 1 at 0, 3, 7 and 15 days. The cleanliness ratings are given in Table 3. TABLE 3 Cleanliness ratings taken after: Example 0 days 3 days 7 days 15 days Ex. 1 8.24 10.00 10.00 10.00 Comp. Ex. 1 9.23 9.65 9.70 9.75 Comp. Ex. 2 9.18 9.37 9.48 9.48

FIG. 1 represents graphically the percent increase in cleanliness ratings over the cleanliness ratings at 0 days for the results of Table 3. It is apparent from Table 3 and FIG. 1 that the cleaning performance of the lubricating oil composition of Example 1 was outstanding. In particular, the blend had the ability to clean both sludge and varnish from the cam-baffle sample. Indeed, it is apparent from the cleanliness ratings that while the initial cleanliness rating was lower for the cam-baffle sample tested with the formulation of Example 1, said lubricating oil composition quickly allowed the cam-baffle to achieve a rating of 10, i.e. representing a completely clean cam-baffle.

Examples 2 and 3 and Comparative Example 1

The lubricating oil compositions of Examples 2 and 3 and Comparative Example 1 were screened using the bench test screener test. Cleanliness ratings for the lubricating oil compositions of Examples and 2 were taken and compared against those of the fully formulated lubricating oil composition of Comparative Example 1 at 0, 2, 4 and 11 days. The cleanliness ratings are given in Table 4. TABLE 4 Cleanliness ratings taken after: Example 0 days 2 days 4 days 11 days Ex. 2 8.24 8.27 9.05 9.40 Ex. 3 8.24 8.82 9.02 9.55 Comp. Ex. 1 8.24 8.24 8.24 8.30

FIG. 2 represents graphically the percent increase in cleanliness ratings over the cleanliness ratings at 0 days for the results of Table 4. It is apparent from Table 4 and FIG. 2 that the cleaning performance of the lubricating oil compositions of Examples 2 and 3 exceeded that of the commercial engine oil of Comparative Example 1 upon which they were based.

Testing Using Modified Sequence VG Test

The lubricating oil compositions of Example 4 and Comparative Example 3 were screened using the modified Sequence VG engine test as hereinbefore described. The cleanliness ratings are given in Table 5. TABLE 5 Cleanliness Rating Comp. Hours Ex. 3 Example 4 0.00 8.08 6.76 24.00 8.64 6.94 48.00 8.65 7.40 72.00 8.65 7.48 96.00 8.60 7.32 120.00 8.72 7.51 144.00 8.74 7.80 168.00 8.74 7.82 192.00 8.72 7.84 216.00 8.65 7.83

The lubricating oil composition of Comparative Example 3 was a commercial engine oil available from the Shell group under the trade designation “HELDI” engine oil, whilst the lubricating oil composition of Example 4 was the same formulation boosted with 3.0 wt. % of “CH-7” product. FIG. 3 represents graphically the percent increase in cleanliness ratings over the cleanliness ratings at 0 hours for the results of Table 5. It is apparent from the results of the modified Sequence VG test on the boosted formulation of Example 4 that said formulation displays better cleaning performance vis-a-vis the standard formulation of Comparative Example 3 in terms of the change in average merit rating of engine parts.

The average end-of-test clean-up for the lubricating oil composition of Comparative Example 3 was 0.57 merit, whereas the average end-of-test clean-up for the boosted lubricating oil composition of Example 4 was 1.07 merit.

While preferred embodiments of the invention have been described herein, it will be understood that various modifications could be made to the components thereof without departing from the scope of the invention. The Examples and other specific descriptions are intended to merely illustrate the invention and are not intended to limit the scope of the claims that follow. 

1. A method of reducing deposits in an internal combustion engine, comprising: lubricating the internal combustion engine with a lubricating oil composition comprising lubricating oil base oil, at least one anti-wear additive, and at least one poly(hydroxycarboxylic acid) amide salt derivative preparable by reaction of an amine and a poly(hydroxycarboxylic acid) of formula (I) Y—CO[O-A-CO]_(n)—OH   (I) where Y is hydrogen or optionally substituted hydrocarbyl group, A is a divalent optionally substituted hydrocarbyl group and n is from 1 to 100, with an acid or a quaternizing agent.
 2. The method according to claim 1 wherein the poly(hydroxycarboxylic acid) amide salt derivatives comprises a compound of formula (III) [Y—CO[O-A-CO]_(n)-Z-R⁺]_(m) pX^(q−)  (III) wherein Y is hydrogen or optionally substituted hydrocarbyl group, A is a divalent optionally substituted hydrocarbyl group, n is from 1 to 100, m is from 1 to 4, q is from 1 to 4 and p is an integer such that pq=m, Z is an optionally substituted divalent bridging group which is attached to the carbonyl group through a nitrogen atom, R⁺ is an ammonium group and X^(q−) is an anion.
 3. The method according to claim 2 wherein R⁺ is a quaternary ammonium group.
 4. The method according to claim 2 wherein A is selected from the group consisting of arylene, alkylene, and alkenylene groups.
 5. The method according to claim 2 wherein there are between 4 and 14 carbon atoms connected between the carbonyl group and the oxygen atom derived from the hydroxyl group.
 6. The method according to claim 2 wherein A includes at least one substituent selected from the group consisting of hydroxy, halo, and alkoxy groups.
 7. The method according to claim 2 wherein X^(q−) is selected from the group consisting of sulfate and sulfonate anions.
 8. The method according to claim 1 wherein Y contains up to 50 carbon atoms and is selected from the group consisting of aryl, alkyl, and alkenyl groups and combinations thereof.
 9. The method according to claim 1 wherein Y is selected from the group consisting of heptyl, octyl, undecyl, lauryl, heptadecyl, heptadenyl, heptadecadienyl, stearyl, oleyl, and linoleyl groups, and combinations thereof.
 10. The method according to claim 1 wherein Y comprises a moiety selected from the group consisting of C₄₋₈ cycloalkyls, polycycloalkyls, aryls, aralkyls, polyaryls, and combinations thereof.
 11. The method according to claim 1 wherein the poly(hydroxycarboxylic acid) is selected from the group consisting of poly(hydroxystearic acid) and poly(hydroxyoleic acid).
 12. The method according to claim 1 wherein the amine is a diamine selected from the group consisting of ethylenediamine and N,N-dimethyl-1,3-propanediamine.
 13. The method according to claim 1 wherein the poly(hydroxycarboxylic acid) amide salt derivative contains sulfur.
 14. The method according to claim 1, further including providing said at least one poly(hydroxycarboxylic acid) amide salt derivative in an amount in the range of from 0.1 to 10.0 wt. %, based on the total weight of the lubricating oil composition.
 15. The method according to claim 1 wherein said lubricating oil composition further comprises at least one detergent selected from the group consisting of alkali metal or alkaline earth metal salicylate, phenate, and sulfonate detergents, and combinations thereof. 